Reinforcing element and fitting for a flexible walled container

ABSTRACT

Fittings of markedly superior crashworthiness for flexible walled liquid containers, particularly fuel tanks for aircraft such as airplanes and helicopters, are made by reinforcing the container wall around such fittings with a plurality of substantially concentric annular turns, such as rings or other shapes utilizing parallel peripheral cords, of substantially inextensible reinforcing material, such as metal wire or textile cords, especially glass fiber cord, of the type commonly used for reinforcing rubber articles. For use in so reinforcing the container, wall reinforcing doilies are provided which comprise an annular sheet of curable but uncured polymeric material embodying (as by attachment to one face of said sheet or by embedment in said sheet or between two such sheets) substantially inextensible reinforcing material disposed as concentric annular turns, such as rings or other shapes utilizing parallel peripheral cords, in a plane generally parallel to the plane of the sheet. Preferably the reinforcing material is wound spirally about the aperture with the adjacent spiral turns in actual physical contact over at least 80 percent of the spiral length.

United States Patent Dorsch [451 Aug. 7, 1973 REINFORCING ELEMENT ANDFITTING FOR A FLEXIBLE WALLED CONTAINER [52] US. Cl 150/8, 285/200,161/35, 161/42 [51] Int. Cl. F16l 5/00 [58] Field of Search 285/200;150/.5, 150/1, 8

[56] References Cited UNITED STATES PATENTS 3,534,987 10/1970 Wallace150/8 X 2,336,552 12/1943 Langford 285/200 X FOREIGN PATENTS ORAPPLICATIONS 480,172 3/1916 France 285/200 Primary ExaminerDonald F.Norton Attorney-Robert J. Patterson [57] ABSTRACT Fittings of markedlysuperior crashworthiness for flexible walled liquid containers,particularly fuel tanks for aircraft such as airplanes and helicopters,are made by reinforcing the container wall around such fittings with aplurality of substantially concentric annular turns,

such as rings or other shapes utilizing parallel peripheral cords, ofsubstantially inextensible reinforcing material, such as metal wire ortextile cords, especially glass fiber cord, of the type commonly usedfor reinforcing rubber articles.

For use in so reinforcing the container, wall reinforcing doilies areprovided which comprise an annular sheet of curable but uncuredpolymeric material embodying (as by attachment to one face of said sheetor by embedment in said sheet or between two such sheets) substantiallyinextensible reinforcing material disposed as concentric annular turns,such as rings or other shapes utilizing parallel peripheral cords, in aplane generally parallel to the plane of the sheet.

Preferably the reinforcing material is wound spirally about the aperturewith the adjacent spiral turns in actual physical contact over at least80 percent of the spiral length.

17 Claims, 3 Drawing Figures PATENTED WWW/Illa 7 REINFORCING ELEMENT ANDFITTING FOR A FLEXIBLE WALLET) CONTAINER BACKGROUND OF THE INVENTION 1.Field of the Invention The field of the invention is that ofcrash-worthy rigid fittings or flexible walled liquid containers,particularly fuel tanks (often called simply fuel cells") for aircraftsuch as airplanes and helicopters, which will withstand crashes withoutfailure. Catastrophic failure of aircraft fuel containers or tankscommonly occurs by reason of the fittings, which are usually of metal,pulling out of the wall of the flexible container. This failure, orrupture, floods the area with fuel resulting in an extremely hazardouscondition.

The fitting constructions developed prior to the present invention,while providing increased resistance to pullout, are costly to installand are not replaceable should they become damaged in the field. Onerequirement of the current military specification for aircraft fueltanks is that the fuel tank be filled with water and dropped from aheight of 65 feet on a non-yielding surface without rupture. Rupture,including failure at or around the fitting, resulting in spillage,constitutes a failure to pass this specification. Fuel tanks havingfittings constructed in accordance with the present invention pass thistest with no difficulty.

2. Description of the Prior Art The most pertinent prior art known tothe inventor is represented by US. Pats. to Smith, No. 2,772,101 (1956);Underwood, No. 3,528,687 (1970) and Wallace et al., No. 3,534,987 (1970)and by a crashresistant fitting known as Fibre Lok" (trademark). None ofthe three patents cited shows a fitting resembling or suggesting thefitting of the present invention. The Fibre Lok fitting comprises anannular ring of rigid material, such as metal, which extends about theaperture in the fuel tank wall. This ring is of substantial radial widthand is provided near its periphery with a series of closely spaced smallholes. Forty to fifty lengths of high strength textile reinforcing cordsare forced through each hole and made to extend outwardly for say from 4to 6 inches in planes substantially parallel to the plane of the ring ina somewhat fanshaped manner. The cords are sandwiched in the fuel tankwall during fabrication and the tank so assembled is cured as anassembly. As is detailed below, comparative drop tests conducted in themanner described above showed the marked superiority of fittings of thepresent invention over Fibre Lok fittings which are believed to be themost crash-resistant fittings developed prior to the present invention.

Typical fuel containers for aircraft have long been made in thefollowing way. The walls of the container are built up (around a formwhich after curing is destroyed and removed) from several plies offabric, almost invariably square woven fabric, coated with a suit ablefuel-resisting curable polymeric material, especially rubbery polymericmaterial such as butadieneacrylonitrile rubbery copolymer, applied tothe fabric by a conventional rubberizing technique such as calen deringor skim coating.v This wall is strengthened around openings for fittingsby adding additional annular plies of curable polymer-coated reinforcingfabric, generally square woven fabric, cut to the proper size and shape,around such openings. These additional plies, referred to as doilies" inthe trade, are coated with a vulcanizable layer of fuel-resisting rubberusually identical with that used in the plies making up the tank wall,so that upon vulcanization all of the doilies and wall plies are bondedfirmly together. Furthermore, the portions of the tank wall contactingthe metallic fitting members (such as members 17 and 22 in FIG. 3 of theaccmpanying drawings) are also tightly bonded on all sides (during thevulcanization of the fuel tank), by virtue of the interposition ofvulcanizable gum stock layers, to the surfaces of the metal fitting.Fuel cells with fittings constructed in this manner, i.e., with doiliesmade from squares woven fabric, are not nearly as crash-resistant as theFibre Lok" construction referred to above.

SUMMARY OF THE INVENTION The invention resides in a novel doily adaptedto be used in reinforcing the wall of a flexible walled liquid containerin the area surrounding a fitting. The invention also resides in a novelfitting construction for such a container and in a flexible walledliquid container em bodying such a fitting construction.

The invention relates particularly to an improvement over the prior artwherein the prior art doilies heretofore employed in makingnon-crashworthy fuel tank fittings, as detailed above under Descriptionof the Prior Art, are replaced by novel doilies which comprise aplurality of closely adjacent substantially concentric annular turns,such as rings or other shapes utilizing parallel peripheral cords, ofsubstantially inextensible reinforcing material, preferably glass fibercord, these novel doilies being disposed in planes which are usuallysubstantially parallel to the surrounding wall of the container. Wherethe wall is curved in the area where the fitting is located, as wherethe: fitting is located in a corner of the tank or in a cylindricalportion of the tank or in a portion having a compound curve, thereinforcing doilies will be correspondingly curved so as to conform tothe contours of the tank wall in the area surrounding the fitting.

The preferred manner of carrying out the invention is to use preformeddoilies made separately in advance from annular sheets of uncured butcurable polymer stock having sandwiched therebetween a spirally woundlayer of such reinforcing material which starts at the inner peripheryof the opening and continues spirally outwardly to the outer edge of thedoily.

Preferably the spiral winding is so carried out that there is actualphysical contact between successive turns for at least percent of thespiral length. This minimum extent of actual physical contact shouldexist for at least 80 percent of the spiral length of each and everytum.

While the preferred doilies made and used in the present invention havebeen described as being spirally wound, the new doily of the inventioncan also be made up of a series of concentric turns, such as circularrings, of reinforcing cord, although at present no economical way isknown by which such a truly concentric cord doily can be manufactured.Because it is much simpler and more practical to wrap the cord spirally,spirally wound doilies are preferred. The slight theoretical advantageof a truly concentric cord doily is not sufficiently great to justifythe vastly greater cost and inconvenience of achieving it. Theexpression substantially concentric annular turns as used herein and inthe appended claims includes both spirally wrapped turns of reinforcingcord as well as concentric individual turns of such cord.

It will be understood that the invention is not limited I to circularfittings but can equally be applied to noncircular fittings. Forexample, it can be applied to oval, elliptical, square or rectangularfittings or to fittings having any other geometrical configuration. Forsuch fittings the spiral winding simply is at least generally concentricwith the fitting. Furthermore, the invention can be applied to fittingsof any type such as inlet fittings, outlet fittings, access openingfittings, etc.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings:

FIG. 1 is a plan view, with the top layer of rubber partly cut away, ofa typical spirally wound circular doily made in accordance with theinvention;

FIG. 2 is a sectional view on the line 22 of FIG. 1, greatly enlarged toshow details; and

FIG. 3 is a vertical section through a wall of a fuel tank having acircular side door fitting installed therein in accordance with thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGS. 1 and 2 ofthe drawings, reference numeral 1 designates a reinforcing doily made inaccordance with the invention. This doily is typically made in thefollowing manner. A layer 2 of gum stock (unvulcanized but vulcanizablefuel-resisting rubber compounded with conventional curatives butcontaining no reinforcing filler such as carbon black) which isapproximately 0.025 inch thick is cut into annular form as shown in FIG.I with an inside diameter appropriately larger than the fitting apertureand with an outside diameter as calculated to support wall stress anddoily-to-wall shear strength. Glass fiber cord 3 or other suitable cordis wound spirally from the inner edge 4 of the central opening to theouter edge 5 of the doily. The surface of gum layer 2 is painted with anappropriate compatible rubber cement just before or during the winding,this adhesive layer being indicated in FIG. 2 by reference numeral 6.The spiral wrapping of the cord is carried out in such a way thatphysical contact between adjacent turns of cord exists for at least 80percent of the spiral length of any given turn. The same type of cementis applied to the upper cord surface after the winding is complete,forming a layer indicated by reference numeral 7. The cemented assemblythus produced is then covered with an annular ring 8 having the sameinside and outside dimensions as ring 2 but considerably thinner,typically 0.008 inch thick, layer 8 being made of the same gum stock aslayer 2. After diffusion of the solvent from the cement layers the doilyl is ready for use in a fitting installation.

Referring now to FIG. 3, a typical fuel container wall 10 is shown asbeing formed from three plies 11 of rubberiz'ed fabric positioned aroundcardboard form 12 (which is disintegrated and removed aftervulcanization). The wall 10 is strengthened about the opening for thefitting by adding additional plies 13 and 14 of conventional rubberizedreinforcing fabric cut to the proper size and shape from theconventional rubberized square woven fabric from which plies 11 arenormally made. The details of the side door and its installation, asdepicted in FIG. 3, are conventional but will now be described forcompleteness. A dowel 15 extending through form 12 cooperates with aplug" 16 to locate the fitting in the assembly until vulcanization ofthe container has been completed. The fitting itself comprises an innermetallic member 17 with circular radially outwardly extending flange 20and axially'extending portion 21, an outer metallic member 22cooperating with flange 20 to fluidtightly seal the laminate of theadjacent wall plies therebetween. This sealing action is the result ofvulcanization of the wall to the metallic members 17 and 22 byinterposed gum stock layers 30, 31 and 32. The side door 23 is heldfluidtightly positioned as shown in FIG. 3 by means of bolts 24threadably engaging portion 21 of inner member 17. Conventional detailsof fittings of this type, such as wedge filler 25, expansion seal 26,and polypropylene separator 27 need not be described in any detail. Aconventional release layer 28, such as a layer of nylon, is used tofacilitate separation of form 12 from the inside of the container.

The improvement of the invention, which has turned the unsatisfactoryuncrashworthy fitting assemblies described above under Description ofthe Prior Art into satisfactory replaceable assemblies and which hasmade it possible to meet the extremely stringent drop test describedabove, is the replacement of the conventional square woven fabricdoilies in the fuel cell fitting assembly with the new spirally wounddoilies 1 constructed as shown in FIGS. 1 and 2. In the typical practiceof the invention as portrayed in FIG. 3, four such doilies l areemployed in alternating fashion in combination with portions of wallplies 11 which are continuations of the rubberized fabric from which thewall plies are formed. The resulting laminate formed from plies l1 anddoilies 1 has its inwardly extending portions fluidtightly held betweenmetallic members 17 and 22. Typically doilies 13 and 14 made ofconventional rubberized square woven wall fabric are positioned on thesides of this laminate and vulcanized thereto as shown in FIG. 3. To aidin the attainment of fluidtightness, layers of gum stock such as thatdescribed above are preferably provided on the surfaces of the radiallyoutwardly extending channel-defining portions of flanges 20 and 22 andon the radially innermost portion of the channel, i.e., around theoutside of axial member 21. These layers of gum stock, indicated byreference numerals 30, 31 and 32, serve to bring about tight bonding ofthe laminate to the metal parts 17 and 22 during the vulcanization ofthe container.

The spiral wound doily of the present invention effectively allows thefuel container wall, i.e., that portion which is contained between themetallic elements of the fitting, to enlarge or change shape, therebypermitting the wall to continue its expansion mode during the passage ofthe primary pressure wave at impact and for a finite, though small,period of time after impact, and remain fluid-tight. Thus, the integrityof the fuel container in the area of the metallic fitting is maintaineddespite the severity of the forces exerted during a crash. 1

Although the flanges of the metallic portions of the fitting, whichfluidtightly contain the laminate of wall plies and doilies about theopening in the fuel container wall, are shown in FIG. 3 as being at anangle with respect to the actual tank wall (i.e., the surfaces of theflanges which contact the faces of the laminate are slanted), they couldeually be parallel to the tank wall in order to reduce the thickness ofthe overall fitting area.

The reinforcing material used in making the reinforcing doilies of theinvention almost invariably is cord of the type commonly used in themanufacture of reinforced rubber articles typified by tires, belts, etc.This cord generally comprises fibrous or filamentary material twistedinto the form of a cord. Several separate cords of such material can beconverted by known cord-forming techniques into a single larger cord.Such a larger cord, as well as original individual cords, can be used asthe reinforcing element from which the novel doilies of the inventionare made.

The cord used in the practice of the invention should be substantiallyinextensible. Examples of substantially inextensible cord elements whichcan be used are those used to form the inextensible tension members inV- belts and toothed positive drive belts, and those from which beltedbreakers for tires are made. The fibrous or filamentary material fromwhich such cords are made may be natural, exemplified by cotton orlinen, or synthetic, exemplified by glass, rayon or polyester, or may beof metal, exemplified by steel, and this material may be in the form ofstaple fiber or in the form of monofilaments.

The cords used in practicing the invention may be impregnated andsurface-coated by solutining," followed by drying, in known manner aswith so-called RFL (resorcinol-formaldehyde resin and rubber latex)solution or other solutioning material which enhances the adhesion ofthe cord to rubber. Likewisethe rubber used in conjunction with thenovel reinforcing elements of the invention can, if desired, becompounded with certain known solid chemical vulcanizing compounds, suchas resorcinol donors and methylene donors. The cord should have lowelongation, high strength and high modulus. The selection of a suitablecord is well within the ordinary skill of the art. Those skilled in theart can readily select a cord which will have the requisite propertiesof strength, elongation, flexibility, etc. for a particular application.Generally speaking, the use of cords of lower strength and higherelongation makes it necessary to use a larger number of doilies for agiven fitting and this is of course undesirable because of greaterweight and volume.

Glass fiber cord is at present preferred for the practice of theinvention. Such cord may be made, for example, from virgin glassfilament having a tensile strength of 500,000 pounds per square inch anda mod ulus of elasticity of 10.5 X 10 psi. An example of a glass fibercord which has been found to be very suitable for use in the inventionis that made from such filament and known in the art as No. 0-75 /5 (nota trademark) glass fiber tire cord having the following properties:

Diameter 0.048" to 0.053" Elongation at Failure 3 to 3.5%

Tensile at Failure 190 to 220 pounds Turns (twist) per inch 1.55

Other types of reinforcing cord can be used in place of glass fibercord. An example is steel cord made by twisting fine steel wires into acord; with steel cord the gauge would generally be somewhat lower thanfor glass fiber cord; well-known techniques such as brassplating thewire can be used to achieve good bonding of the rubber thereto.

Results of Full Scale lDrop Tests Thirteen full scale drop tests ofAH-lG helicopter fuel cells containing 136.5 gallons of water from aheight of 65 feet on an unyielding surface were conducted in thechronological order and with the results shown in the following table:

Number of Type of Fuel Cells Fitting Dropped Fitting Location Results"Fibre Lok 2 Side and bottom Wall failure at of cell fitting and fittingfailure 2 Side of cell Wall failure at fitting 2 Side of cell Wallfailure at fitting 3 Side of cell Wall failure at fitting 3 Fittingsremoved Passed drop test from side of cell and relo cated at top That ofthe invention 1 Side of cell Passed drop test The fitting which was usedin the last drop test in the above table, which passed after ninesuccessive failures using the Fibre Lok design, was made in accordancewith the invention with spiral wound type No. G- 5/5 glass fiber tirecord doilies. Such a fitting allows the wall stress to be carried aroundthe fitting rather than terminating at the fitting boundary. With theinvention the wall is not physically attached to the fitting exceptthrough bond and can therefore expand freely during the passage of thedynamic pressure wave; the wall stress is transferred to the series ofspirally wound doilies through bond shear and is thus transmitted aroundthe fitting.

Advantages Since the tests reported in the above table were run, 13 morefuel cells of the above type, and made with spirally wound doiliesaccording to the invention, were subjected to the drop test. Many ofthese additional cells contained nine fittings installed in accordancewith the invention. All of these cells passed the drop test except twowhich failed only because the fittings embodied domenuts of a newdesign; this problem, which was not related to the present invention,was quickly resolved by increasing the head thickness of the domenuts.

The fitting of the present invention is now qualified and approved byBoeing Vertol (trademark) for use in the CH-47 helicopter auxiliary andmain tanks, from the standpoint of drop tests, although not yet from thestandpoint of unrelated fuel soak and slosh tests.

The doily reinforcement of the invention prevents rigid attachment ofthe fuel tank wall to the extreme fitting boundaries because the primarywall stresses develop in the hoop direction during the compression phaseof cell impact. During this time the meridional wall stresses arenegative.

As the pressure wave rises vertically through the unobstructed cellwall, hoop strain occurs harmoniously with wall stress. With prior artconstructions, an obstruction in the wall of the cell (e.g., fittings,etc.) which results in reduced elongation confines the freely expandingwave front giving rise to wall stress amplification and ultimate failureat the point of greatest strain reduction. This does not happen withfittings embodying the present invention.

Prior art constructions are marginally unsatisfactory with the smallerfittings, that is, those up to about 4-5 inches in diameter, andgenerally unsatisfactory with fittings larger than this. In contrast,with the present invention, there appears to be no practical limitationon the size of the fitting; this is very advantageous because it makesit possible to install very large fittings without risk of failure.

In addition to the unobvious advantage that it enables the fuelcontainers to easily pass the stringent drop test, the present inventionsignificantly reduces building time. The fitting of the presentinvention is inexpensive to produce and requires very little labor toinstall. In contrast, the preparation of the Fiber Lok fitting is verytedious and results in high labor costs; this type of fitting is alsovery costly to produce because of the large number of peripheral holesand the exacting finish requirements.

The ease with which fittings of the present invention can be replacedshould they become damaged through use or misuse during building or inthe field represents a most significant and important advantage of thepresent invention. It is easy to remove a damaged or defective fittinginstalled in accordance with the present invention and to install areplacement therefor. Such removal can be effected by debonding themetal fitting parts from the laminate and removing them. New metal partsare installed as required, using a self-vulcanizing rubber cement toeffect rebonding of the laminate to the walls of the channel formed bythe new metal parts. In this way a costly fuel tank which wouldotherwise have to be discarded can be put into perfect condition at lowexpense. This advantage of ease of replaceability of fittings made inaccordance with this invention cannot be achieved with the Fibre Lok"type of fitting because with the latter the fan-shaped bundles ofreinforcing cords cannot be removed and replaced with anythingapproaching the necessary precision.

Another marked advantage of the present invention flows from the factthat the number of doilies used is a function of the wall stress or wallload due to impact. With the Fibre Lok type of fitting only a maximumnumber of cords can be used and if the wall load exceeds the cordstrength failure occurs and there is no way of obtaining greaterfitting/wall strength. With the present invention to get morefitting/wall strength it is only necessary to add more of the noveldoilies of the invention.

Another problem with the Fibre Lok type of fitting is that during thebuilding operation it is very difficult or even impossible to maintainequal tension on all of the cords being buried in the cell wall.Consequently the higher tensioned cords fail first, then lower tensionedcords, and so on, resulting in progressive failure and lowering of thefitting efficiency. This cannot happen with the spiral wound doilies ofthe present inventron.

While the invention has been described with particular reference toinstallations made with vulcanizable rubber as the polymeric material,it will be understood that the invention is not limited thereto but canbe carried out with other curable fuel-resisting polymeric materialssuch as curable polyurethane materials.

Having thus described my invention, what I claim and desire to protectby Letters Patent is:

l. A flexible walled liquid container having a fitting disposed in anaperture of a wall thereof and comprising a plurality of parallelreinforcing doilies in the wall surrounding said aperture, said doiliescomprising substantially concentric annular turns of substantiallyinextensible reinforcing material disposed about the aperture.

2. A container as defined in claim 1 wherein said reinforcing materialis selected from the group consisting of textile cord and metal cord.

3. A flexible walled liquid container having a fitting disposed in anaperture of a wall thereof and comprising a plurality of parallelreinforcing doilies in the container wall surrounding said aperture,said doilies comprising substantially inextensible reinforcing materialwound spirally about the aperture.

4. A container as defined in claim 1 wherein said reinforcing materialis selected from the group consisting of textile cord and metal cord.

5. A container as defined in claim 3 wherein there is physical contactbetween adjacent turns of said reinforcing material over at leastpercent of the spiral length.

6. A container as defined in claim 5 wherein said reinforcing materialcomprises glass fiber cord.

7. A flexible walled liquid container having a fitting disposed in anaperture of a wall thereof and comprising a plurality of parallelreinforcing doilies in the container wall surrounding said aperture,said doilies comprising a plurality of substantially concentric annularturns of substantially inextensible reinforcing material and beingdisposed about the aperture in planes which are generally parallel tothe plane of the adjacent container wall.

8. A flexible walled liquid container having a fitting disposed in anaperture of a wall thereof and comprising a plurality of parallelreinforcing doilies in the container wall surrounding said aperture,said doilies comprising substantially inextensible reinforcing materialwound spirally about the aperture and being disposed in planes which aregenerally parallel to the plane or planes of the adjacent containerwall.

9. A container as defined in claim 8 wherein there is physical contactbetween adjacent turns of said reinforcing material over at least 80percent of the spiral length.

10. A container as defined in claim 9 wherein said reinforcing materialcomprises glass fiber cord.

11. In a fitting for a flexible walled liquid container having anaperture surrounded by a thickened rim portion, said fitting comprising:

A. a pair of opposed rigid rings;

B. means for fastening said rings together in face-toface relationship;

C. said rings having radially outwardly extending portions definingtherebetween a radially outwardly facing channel;

D. said rings being locked in position in the wall of the container andabout said aperture; and

E. means filling said channel and fixedly and fluidtightly held betweensaid channel-defining portions, said means comprising a laminatecomprising alternately disposed parallel doilies and portions of fabricwhich are continuations of the fabric from which the wall of thecontainer is formed, said doilies and portions of fabric beingfluidtightly bonded to one another; the improvement wherein said doiliescomprise a plurality of closely adjacent substantially concensaidsubstantially inextensible reinforcing material wound spirally in planessubstantially parallel to said channel-defining portions.

16. A construction as defined in claim 15 wherein there is physicalcontact between adjacent turns of said reinforcing material over atleast percent of the spiral length.

17 A construction as defined in claim 16 wherein the elements of saiddoilies are bonded together into said laminate by a cured fuel-resistingpolymeric material which is compatible with fuel-resisting polymericmaterial used in the wall of the container.

2. A container as defined in claim 1 wherein said reinforcing materialis selected from the group consisting of textile cord and metal cord. 3.A flexible walled liquid container having a fitting disposed in anaperture of a wall thereof and comprising a plurality of parallelreinforcing doilies in the container wall surrounding said aperture,said doilies comprising substantially inextensible reinforcing materialwound spirally about the aperture.
 4. A container as defined in claim 1wherein said reinforcing material is selected from the group consistingof textile cord and metal cord.
 5. A container as defined in claim 3wherein there is physical contact between adjacent turns of saidreinforcing material over at least 80 percent of the spiral length.
 6. Acontainer as defined in claim 5 wherein said reinforcing materialcomprises glass fiber cord.
 7. A flexible walled liquid container havinga fitting disposed in an aperture of a wall thereof and comprising aplurality of parallel reinforcing doilies in the container wallsurrounding said aperture, said doilies comprising a plurality ofsubstantially concentric annular turns of substantially inextensiblereinforcing material and being disposed about the aperture in planeswhich are generally parallel to the plane of the adjacent containerwall.
 8. A flexible walled liquid container having a fitting disposed inan aperture of a wall thereof and comprising a plurality of parallelreinforcing doilies in the container wall surrounding said aperture,said doilies comprising substantially inextensible reinforcing materialwound spirally about the aperture and being disposed in planes which aregenerally parallel to the plane or planes of the adjacent containerwall.
 9. A container as defined in claim 8 wherein there is physicalcontact between adjacent turns of said reinforcing material over atleast 80 percent of the spiral length.
 10. A container as defined inclaim 9 wherein said reinforcing material comprises glass fiber cord.11. In a fitting for a flexible walled liquid container having anaperture surrounded by a thickened rim portion, said fitting comprising:A. a pair of opposed rigid rings; B. means for fastening said ringstogether in face-to-face relationship; C. said rings having radiallyoutwardly extending portions defining therebetween a radially outwardlyfacing channel; D. said rings being locked in position in the wall ofthe container and about said aperture; and E. means filling said channeland fixedly and fluidtightly held between said channel-definingportions, said means comprising a laminate comprising alternatelydisposed parallel doilies and portions of fabric which are continuationsof the fabric from which the wall of the container is formed, saiddoilies and portions of fabric being fluidtightly bonded to one another;the improvement wherein said doilies comprise a plurality of closelyadjacent substantially concentric annular turns of substantiallyinextensible reinforcing material.
 12. A construction as defined inclaim 11 wherein said reinforcing material is selected from the groupconsisting of textile cord and metal cord.
 13. A construction as definedin claim 11 wherein adjacent turns of said reinforcing material are inphysical contact with one another over at least 80 percent of theirannular length.
 14. A construction as defined in claim 13 wherein saidreinforcing material comprises glass fiber cord.
 15. A construction asdefined in claim 11 wherein said substantially concentric annular turnscomprise said substantially inextensible reinforcing material woundspirally in planes substantially parallel to said channel-definingportions.
 16. A construction as defined in claim 15 wherein there isphysical contact between adjacent turns of said reinforcing materialover at least 80 percent of the spiral length.
 17. A construction asdefined in claim 16 wherein the elements of said doilies are bondedtogether into said laminate by a cured fuel-resisting polymeric materialwhich is compatible with fuel-resisting polymeric material used in thewall of the container.